Saturday, February 26, 2011

Project 18 - Dual 8-Bit Binary Counters

Looks like I'll be paying a visit to my local electronics store on Monday... I believe that one of my 595 chips is damaged. Let me explain.

I wired up the circuit as shown in Figure 6-4... it's a fairly logical layout if you understand Project 17. When I fired it up, I could get the LEDs on the left (sorry, I had to use all red LEDs) to start counting down from 255... but the LEDs on the right (connected to new 595 chip) weren't lighting up.

I tried quite a few things:

1. I switched out the LEDs with a few random ones (green, yellow, red mix) but no luck.
2. I switched out the LEDs on the left (that I knew worked) with the ones on the right... no luck.
3. I reversed the two 595 chips and the LEDs on left stopped working but ones on right did work.


Then I went back to my wiring... just in case. The wiring was fine, but given that swapping the 2 chips also reversed the LEDs lighting up, I'm fairly certain I've got a damaged HC595. But it's my fault... when I was inserting the 2nd HC595, one of the pins got bent... I used my small pliers to fix it. But after removing the chips numerous times with small bends in various pins, I'm certain that one of the 595s has died at my hands.

RIP HC595 #2...

This also means that Project 19 is on hold until I can get a replacement. Scratch that - if I can find them locally, I'll likely buy 3 or 4 to have extras. And I'm going to invest in a chip puller.

On a different note... my wife got me a Hakko 936 solder station for Valentine's Day (yes, she's pretty awesome) that I've been playing with and loving. It's got a dial-in temp gauge on front, however, that's been tricky for me as the documentation came with nothing related to finding the proper temps for solder.

I was in ACK Electronics last week to get a few spare tips (should have bought some spare 595s!) and mentioned the issue to Scott who works there... he pulled out this great little card (from 1977) that, among other things, has a sliding scale that allows you to find the melting temp in C and F for different mixes of solder. Look at one of the photos and you can see that I've selected a 60/40 mix of tin/lead and the guide gives me a range of 361-374F for the melting temp. Scott gave me the card to keep and it's now sitting next to my 936.

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